The long-range aim is to develop an effective and practical immunization against cholera. Progress in this direction should also add to knowledge of mucosal immune mechanisms and aid efforts to immunize against other mucosal infections. The proposed studies, which extend our prior work on this subject, will use current knowledge of the mucosal secretory immune system and the pathogenesis of cholera and a recnetly developed, nearly ideal, adult rabbit model of cholera to achieve the following: 1.) Develop optimally effective and safe oral immunizing regimens for cholera using nonliving antigens (e.g. procholeragenoid, cholera lectin, and a crude toxin-free mixture of antigens). These will be used singly and in combinations with the aim of evoking lasting synergistic protection against colonization and disease. Oral adjuvants, including antigen-containing liposomes, will be tested for their ability to enhance immunogenicity of oral antigens. And the effectiveness of the best immunization regimens will be compared with protection evoked by colonization with virulent or avirulent live V. cholerae. 2.) More precisely define how mucosal immunity to cholera is mediated and sustained. The kinetics of mucosal colonization in immune and nonimmune rabbits will be precisely define by methods that assess vibrio distribution at the mucosal surface and measure multiplication or death of the challenge inoculum as it transits the gut. The anticolonization effects of specific immunization regimens will be determined. The possibility that immune-mediated mucus release aids in preventing colonization will be studied. And the effect of lactation on maternal immunity, and of lactational phase on transfer of immunity to infants, will be determined. Throughout these studies, protection against disease and resistance to colonization will be compared with specific mucosal (or milk) immune responses measured in gut (or mammary gland) biopsies or in intestinal washings or mammary secretions. The results of these studies, which could not be done in such detail in humans, should find direct application in guiding efforts to develop an effective oral vaccine for cholera.